1. Technical Field
The present invention relates to an axial flow fan in which the shape of a rotating blade of an impeller and the shape of an inner surface of a venturi casing surrounding an outer periphery of the impeller in a radial direction are optimized.
2. Description of Related Arts
An axial flow fan includes a cylinder-shaped venturi casing at an outer periphery of an impeller in a radial direction for forming an axial flow in conjunction with the impeller. The impeller is mounted on a rotating shaft of a rotary drive device. The axial flow fan is widely used as a cooling fan of a device such as a server because of its simple structure.
The axial flow fan typically has the blow characteristics in that air volume is large and a static pressure is small. To improve such blow characteristics of the axial flow fan, the shape of a rotating blade of the impeller and the structure of the venturi casing have been devised in various ways.
As a technology related to the shape of the rotating blade of the impeller, an axial flow fan is disclosed in which a line extending from a center of rotation of the impeller and passing an intersection of a trailing edge of a blade and a radially outer edge thereof is arranged closer to the side of a rotating direction, compared to another line extending from the center of rotation of the impeller and passing an intersection of a leading edge of the blade and a boundary between a hub and the blade. Furthermore, in this axial flow fan, a camber ratio from a radius of the hub to a radius of the radially outer edge of a blade, which is minimum at a joint with the hub across the blade, monotonically increases to be maximum at the radially outer edge of the blade (see Japanese Patent Application Laid-Open Publication No. 2008-111383, for example).
Further, as a technology related to the structure of a venturi casing, a blower device is disclosed in which a cross-sectional surface of an orifice (venturi casing) includes a partial or whole arc portion on a suction side, a linear portion, and a discharge-side arc portion, and in which the arc radius of the suction-side arc portion is formed larger than the arc radius of the discharge-side arc portion (see Japanese Patent Application Laid-Open Publication No. 5-133398, for example).
Incidentally, the axial flow fan in Japanese Patent Application Laid-Open Publication No. 2008-111383 achieves noise reduction by forming a flow parallel to the rotating shaft on a plane including the rotating shaft while maintaining static pressure by improving the shape of the rotating blade of the impeller.
On the other hand, the blower device in Japanese Patent Application Laid-Open Publication No. 5-133398 achieves noise reduction while obtaining a large air flow by forming the arc radius of the suction-side arc portion larger than the arc radius of the discharge-side arc portion.
However, operation characteristics of the axial flow fan are affected by interaction between the shape of the rotating blade of the impeller and the structure of the venturi casing. Therefore, noise reduction and high static pressure may not be achieved in an actual use area even though only the shape of the rotating blade of the impeller or the structure of the venturi casing is set individually.
The present invention has been made in view of the foregoing circumstances, and an object of the present invention is to provide an axial flow fan capable of achieving noise reduction and high static pressure in the actual use area.